The purpose of this project is to study the physical properties of a wide variety of biological macromolecules, with the goal of correlating these properties to the structure and function of the macromolecules. The emphasis is on the thermodynamics of the interactions of these macromolecules and on their molecular size and shape. Analytical ultracentrifugation and mathematical modeling are the principal research techniques used. Studies on HIV reverse transcriptase have been directed toward investigating the thermodynamics of the homogeneous association of the P66 subunit, and the heterogeneous association of P66 with the P51 subunit. Studies on chromagranin A have been directed toward investigating the effects of pH and calcium ion concentration on the thermodynamics of the aggregative properties of the molecule, and toward studying these same factors for various peptide domains of the molecule. Studies on DNA polymerase-b have been directed toward investigating the conformational properties of the molecule by fluorescence and ultracentrifugal studies, and toward investigating the interaction of the enzyme with nucleic acids. Studies on CEB-63, a leucine-zipper peptide, have been directed toward determining the thermodynamic parameters characterizing its reversible aggregation.